题解 | #数字字符串转化成IP地址#

import java.util.*;


public class Solution {
    /**
     * 
     * @param s string字符串 
     * @return string字符串ArrayList
     */
    public ArrayList<String> restoreIpAddresses (String s) {
        // write code here
        ArrayList<String> res = new ArrayList<>();
        int l = s.length();
        for(int i = 1;i<4&&i<l-2;i++){
            for(int j = i+1;j<i+4&&j<l-1;j++){
                for(int k = j+1;k<j+4&&k<l;k++){
                    if(l-k >= 4){
                        continue;
                    }
                    String a = s.substring(0,i);
                    String b = s.substring(i,j);
                    String c = s.substring(j,k);
                    String d = s.substring(k);
                    if(Integer.parseInt(a)>255 || Integer.parseInt(b)>255 || Integer.parseInt(c)>255 || Integer.parseInt(d)>255){
                        continue;
                    }
                    if((a.length() != 1 && a.charAt(0) == '0') || (b.length() != 1 && b.charAt(0)=='0') || (c.length() != 1 && c.charAt(0) == '0')||(d.length() != 1 && d.charAt(0) == '0')){
                        continue;
                    }
                    String temp = a+"."+b+"."+c+"."+d;
                    res.add(temp);
                }
            }
        }
        return res;
    }
}